The Denver Broncos continue to deal with serious injury issues at center.

NFL.com's Ian Rapoport reported Sunday, per a source informed of the injury, that Dan Koppen is done for the season after suffering a torn anterior cruciate ligament in his left knee. Koppen was carted off the field after hearing a pop in the knee during training-camp practice.

Koppen, 33, signed with the Broncos last month after J.D. Walton was lost for the season after suffering a setback in his recovery from a dislocated ankle. Koppen filled in admirably for Walton last season, starting 12 games.